Recently, by using the ventilation fan installed in the ceiling, the ventilation fan for duct for exhausting the indoor foul air outdoors through the duct for improving the environment of living space is becoming popular. At the same time, the concern about the indoor interior quality is being heightened year after year. Further, the concern about the work for installing the ventilation fan for duct is also heightened year after year.
A conventional example of ventilation fan for duct is described while referring to FIG. 4 through FIG. 6. As shown in FIG. 4 through FIG. 6, at the back side of a decorative plate 102 provided at the indoor side intake port of a ventilation fan main body 101, a spring 103 for attaching to the ventilation fan main body 101 is provided, and an adapter 105 for connecting to an exhaust duct 104 is fitted to the side of the ventilation fan main body 101. The junction surface of an exhaust port 106 at the side of the ventilation fan main body 101 and the adapter 105 for connecting to the exhaust duct 104 is a flat surface because the shape of the ventilation fan main body 101 is in a box shape. Besides, since the shape of a scroll 107 which is a part of the ventilation fan main body 101 is in a spiral shape, and hence a flat portion 108 is formed outside, but to form the box shape of the ventilation fan main body 101, a wall 109 is provided, and a motor 112 for driving blades 111 is provided in a top plate 110.
When installing such conventional ventilation fan for duct, the exhaust duct 104 is preliminarily installed at the position for installing the ventilation fan for duct, and an opening 114 for inserting the ventilation fan main body 101 is provided in a ceiling 113, and a wood frame 115 for fixing the ventilation fan main body 101 is assembled behind the ceiling of the opening 114. In such state, first the adapter 104 is inserted into the opening 114, and fixed to the exhaust duct 104 by taping or the like, and fixed to the wood frame 115 by screws. Then, while fitting the ventilation fan main body 101 into the adapter 105, it is inserted into the opening 114, and is fixed to the wood frame 115 by screws. Finally the spring 103 of the decorative plate 102 is inserted into a slot 116 provided in the ventilation fan main body 101, and the decorative plate 102 is fitted to the ventilation fan main body 101.
In such conventional ventilation fan for duct, since the shape of the ventilation fan main body 101 and opening 114 is square, the mounting direction of the decorative plate 102 is controlled at 90-degree increments. Hence, there was a strange feel between the design of the decorative plate 102 and the pattern of the ceiling 113. Moreover, the junction surface of the exhaust port 106 at the side of the ventilation fan main body 101 and the adapter 105 for connecting to the exhaust duct 104 is a flat surface, and the flat surface is not stable in shape, and a gap may be formed on the junction surface to leak wind, and therefore a packing or other part must be used. When inserting the ventilation fan main body 101 into the opening 114 while fitting into the adapter 105, to prevent the flat portion 108 from hitting against the opening 114 of the ceiling 113 to make it hard to insert, the wall 109 is provided to form the ventilation fan main body 101 in a box shape, which causes to increase the material cost.